Spektrum still has an issue with brownouts that other brands don't. Yes it's true that any 2.4ghz receiver will reboot if the voltages gets low enough, but the threshold is set lower on all the other brands. Spektrum reboots at 4 volts, which one can easily reach with a 4.8 battery that is in good condition and a second of high servo loading. I've seen testing where Futaba will work down to 2.5v, and Airtronics says their receivers will work with full range down to 2v. I don't know about Hitec, but since there haven't been any anecdotes that I'm aware of about them rebooting I assume their threshold is pretty low too.
When Spektrum was first released, lots of people lost planes due to the 3 second reboot time after falling below 4 volts. Mind you, that was planes flying with the 4.8v battery that Spektrum included with the system. No warnings about voltage sag were given in the manual or the Spektrum website until a rash of complaints started to surface. Spektrum's response was to make the reboot time quicker instead of making the voltage threshold lower, so at best it's a bandaid. So if you run 4.8v packs with Spektrum you still can get brownouts that will take about 1/2 second to reboot. If that happens at the bottom of a loop it will still cost you an airplane.
Everyone is entitled to their own opinions, but I'll never fly Spektrum or JR (the parent company) equipment. They released a product line with a major flaw and only admitted the issue after the complaints were too well known for them to ignore it. There was a big spike in complaints about the Dx8 radio having unexplained crashes too so apparently that's their business model. They either didn't do any product testing in the real world or they just ignored the issues in order to get into the market first. With systems that were reliable from the start from Airtronics and Hitec (Futaba had an issue with heat causing shutdowns which they promptly fixed) I don't see why we as a community haven't put Spektrum out of business.